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series of 14 and

Uranium-238 / Lead-206

4.50 billion years

emissions

Uses for Radioactive Isotopes

Radioactive isotopes have proven to be useful tools for scientists. Because the emissions from radioactive

decay can be detected with film, Geiger counters or other sensitive instruments, it is possible to locate them

and measure the amount present.

Medical professionals often use radioactive isotopes to visualize certain parts of the body. For example,

stress fractures cannot be seen with standard X-rays until weeks after the injury when the bone has begun to

heal. However, if necessary, doctors can use certain radioisotopes that are preferentially taken up by bone

tissue to visualize such injuries much earlier. One such chemical is a phosphate compound of Technetium-99m

(Tc-99m).

The half-life for Technetium-99m is ________________. [Use Table 2]

the

2. If one is having such a bone scan done, the Tc-99m compound is administered intravenously, and

scan is done three hours later

. Assume that none of the Tc-99m is eliminated from the body (e.g., in

urine or feces) during this time period.

How many half-lives (HL) have passed when the scan is done? ____________ HL

3. Use the information from questions 1 and 2 to calculate what percentage of the Tc-99m remains in the

body after the scan is done. Use three significant figures for the percentage and show your work!

________%

Smoke detectors also take advantage of radioactivity by using Americium-241, an artificially produced

radioactive isotope that emits alpha particles and low energy gamma rays. The alpha particles are absorbed

within the detector and cannot escape. (Although the gamma rays do escape, the amount of Americium-241

used in smoke detectors is so minute that the radiation released is much less than natural background levels

of radiation.) The alpha particles in the detector ionize nitrogen and oxygen molecules entering the detector's

ionization chamber from the surrounding air. A low-level electrical voltage collects these resulting ions,

creating a steady electric current. Smoke or hot air entering the chamber will absorb the alpha particles,

altering the number of ionized particles and the electric current, which triggers the alarm.

The half-life for Americium-241 is ________________. [Use Table 2]

2. How many half-lives have passed after 100 years? _________ HL (use three significant figures)

3. Use the information from questions 1 and 2 to calculate what percentage of the Americium-241 remains

after 100 years. Use three significant figures for the percentage and show your work!

_______%

4. A smoke detector requires about 0.3 micrograms of Americium-241 to work properly. If the smoke

detector originally contains 0.5 microgram of Americium-241, does it contain enough radioactive material

to function properly after 100 years? Explain your answer.

GCC CHM152LL: Nuclear Chemistry

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Gcc Chm152ll: Nuclear Chemistry - Radioactivity, Decay, Dating, And Other Hazards Worksheets Page 6